SumType! seemingly results in cryptic error, with dub suggesting to make an issue ticket

[user456]

On Tuesday, 30 May 2023 at 08:42:38 UTC, Gimbles wrote:
> My code is this
> [...]
> Should I make an issue for this as it suggests?

100% yes. This an "Internal Compiler Error" (ICE), meaning the 
compiler has crashed.
Open a ticket here : 
https://issues.dlang.org/show_bug.cgi?id=23935

with a title like "ICE caused by std.sumtype", and paste the test 
case.